1. Field of the Invention
The present invention relates to a control apparatus for use in an automobile air-conditioner for controlling the supply mode of air to be blown into a vehicle compartment.
2. Description of the Prior Art
Japanese Patent Publication No. 59-19849, for example, discloses a conventional control apparatus for automobile air-conditioners. In the known control apparatus, a total signal which corresponds to a thermal load is calculated based on the temperature in the vehicle compartment, a setting temperature, etc. The thus calculated total signal is used to determine a prescribed mode pattern according to which the air blow-off mode is automatically changed to shift between a vent (VENT) mode, a bi-level (B/L) mode and a heat (HEAT) mode. Such automatic control however does not apply to the defrosting operation of the air-conditioner.
This is because when the windshield becomes frosted, the driver is able to initiate a defrosting operation at his own discretion, in preference to any other operations, thereby clearing up the windshield immediately.
This manual defrosting operation is in fact advantageous in case of emergency. However, if a defrost/heat(DEF/HEAT) mode for keeping the driver's feet warm and also for keeping the windshield free of frost is controlled manually, a problem would arise in that the windshield still become frosted even when the air-conditioner is set to operate at the HEAT mode during the winter season or when the outside air temperature is low. In this instance, it is necessary for the driver to change the mode of operation of the air-conditioner from the HEAT mode to the DEF/HEAT mode to thereby prevent the windshield from frosting over. Conversely, if the DEF/HEAT mode continues for a long period of time, the driver's head is heated gradually and hence the driver is forced to change the mode of operation of the air-conditioner. With this frequent mode change, an automated operation of the air-conditioner in all seasons is difficult to achieve.